1. Field of the Invention
The present invention relates to a wiring substrate which allows various electronic components such as a crystal oscillator to be mounted on a surface thereof so that the electronic components can be sealed, and a multi-piece wiring substrate including a plurality of the wiring substrates.
2. Description of Related Art
For example, a package for piezoelectric oscillator is proposed which includes a substrate formed by an insulating sheet, a pair of oscillation piece mount electrodes formed on a front surface of the substrate, four external connection electrodes respectively formed on four corner sides of a rear surface of the substrate, and a metal ring having a rectangular frame shape and fixed along the periphery of the front surface (for example, see Patent Document 1). Lower ends of a pair of vias, whose upper ends are respectively connected to the oscillation piece mount electrodes and which penetrate the substrate, are respectively connected to a pair of lead-out electrodes extending toward the center of the rear surface from a pair of the external connection electrodes diagonally located on the rear surface.
According to the above package for piezoelectric oscillator, even if a thin substrate is used, in a manufacturing process of a piezoelectric oscillator using the package, or the like, crack is less likely to occur and reliability is ensured. Therefore, the package and the piezoelectric oscillator with a reduced size and a reduced thickness can be obtained.
However, in the case of the package for piezoelectric oscillator disclosed in Patent Document 1, in the first embodiment shown in FIGS. 1(a) to 1(c), when a plurality of the packages are arranged in series along a right-left direction in FIGS. 1(a) to 1(c) and current is applied for covering a surface of each conductor exposed to outside with a metal plating film, the current flows through: a first route of external connection electrode 17c→via 16→metal ring 15→via 16→external connection electrode 17d→external connection electrode 17a of adjacent package→lead-out electrode 18→via 14a→oscillation piece mount electrode 12a; a second route of external connection electrode 17a→lead-out electrode 18→via 14a→oscillation piece mount electrode 12a; and a third route of external connection electrode 17b→lead-out electrode 18→via 14b→oscillation piece mount electrode 12b. As a result, in the case of the package for piezoelectric oscillator, when a surface of each conductor exposed to outside is to be covered with a metal plating film in each individual package, a plurality of routes of plating currents are needed. Further, in a multi-piece configuration, it is impossible to cover a surface of each conductor exposed to outside with a metal plating film per a plurality of packages. Therefore, it is significantly difficult to provide a package for piezoelectric oscillator in which a surface of each conductor exposed to outside is reliably covered with a metal plating film.